In biological purification of waste waters which contain organic solids, sediments are formed which are so firm that anaerobic zones occur within them. This leads to the creation of offensive odors and sedimentation. Dissolved oxygen is required to prevent the formation of these offensive odors and to biologically break down the organic matter within the water. Moreover, a certain amount of dissolved oxygen is required to sustain various aquatic organisms. Increasing the dissolved oxygen content of other substances, such as sludge, is also necessary.
Aeration apparatus are used to increase the dissolved oxygen content of the treated substance and thereby purify it. One type of aeration apparatus is a propeller aspirator aerator. These devices use an electric motor driven rotating propeller disposed below the surface of the substance being treated. The propeller draws in atmospheric air from an intake port through a draft tube and discharges it into the substance.
As is apt to happen with subsurface propeller-type devices, vortices are created, In the context of an aeration apparatus, vortices are undesirable as they decrease the speed and efficiency of operation. To combat this problem vortex shields have been developed for aerators. These shields prevent the formation of vortices adjacent the propeller in the substance in which the propeller is driven. In prior art embodiments of vortex shields, the shield is rigidly affixed to the aerator so as to reside, in part, above the aerator propeller when the aerator is in operation. These shields are either flat or curved around the aerator shaft.
These prior known devices have a number of disadvantages, all of which are alleviated and eliminated by the present invention. The rigidly affixed vortex shields catch material which floats in the water. Since the shields are disposed under the surface of the water, it is difficult, if not impossible to locate any problems with the shield. The shields also are not able to eliminate every vortex created. Often a vortex forms in a non-vertical direction and evades the vortex shield. Also when a vortex escapes the shield it sometimes vibrates the shield and tears it off. The mobile vortex shield disclosed below solves these problems.